Because, like most things in this country which involve long term vision, successive governments simply kick the can down the road knowing that when the excrement finally does hit the air conditioning, they will have long since sailed off into the sunset and a happy retirement, giving after-dinner speeches which bring in far more than they ever earned in politics.
There is one desalination plant in East London, at Beckton. It cost £250m to build and as far as I know, apart from testing it when it was completed in 2010, it has never been used. It was not used during last summer’s dry spell as it was “undergoing essential maintenance work.” How something that had hardly been used had to undergo maintenance at the very time of year it was most likely to be required remains a mystery. Some critics suggest it is the cost of running it which means it is effectively mothballed for now. But I couldn’t possibly comment on that.